Propulsion system for an aircraft

ABSTRACT

A propulsion system for an aircraft includes an electric power source and an electric propulsion assembly having an electric motor and a propulsor, the propulsor powered by the electric motor. The propulsion system also includes an electric power bus electrically connecting the electric power source to the electric propulsion assembly. The electric power source is configured to provide electrical power to the electric power bus, and the electric power bus is configured to transfer the electric power to the electric propulsion assembly at a voltage exceeding 800 volts.

FIELD

The present subject matter relates generally to an aircraft propulsionsystem, and more particularly to an aircraft propulsion system includingan electric propulsion assembly and an electric power bus.

BACKGROUND

A conventional commercial aircraft generally includes a fuselage, a pairof wings, and a propulsion system that provides thrust. The propulsionsystem typically includes at least two aircraft engines, such asturbofan jet engines. Each turbofan jet engine is mounted to arespective one of the wings of the aircraft, such as in a suspendedposition beneath the wing, separated from the wing and fuselage.

More recently, propulsion systems have been proposed of ahybrid-electric design. With these propulsion systems, an electric powersource may provide electric power to an electric fan to power theelectric fan. These systems have been designed to operate at relativelylow voltages (e.g., at or below 270 volts), as when the aircraftincorporating the propulsion system is operated at high altitudes, as istypical during cruise operation, a reduction in ambient air pressure maymake higher voltage systems unwieldy.

However, the inventors of the present disclosure have found thatutilizing a relatively low voltage system may be undesirable forsituations requiring any substantial amount of power given a weight ofthe cables required to carry the increase in electrical current.Accordingly, a propulsion system capable of overcoming these obstacleswould be useful.

BRIEF DESCRIPTION

Aspects and advantages of the invention will be set forth in part in thefollowing description, or may be obvious from the description, or may belearned through practice of the invention.

In one exemplary embodiment of the present disclosure, a propulsionsystem for an aircraft is provided. The propulsion system includes anelectric power source and an electric propulsion assembly having anelectric motor and a propulsor, the propulsor powered by the electricmotor. The propulsion system also includes an electric power buselectrically connecting the electric power source to the electricpropulsion assembly. The electric power source is configured to provideelectrical power to the electric power bus, and the electric power busis configured to transfer the electric power to the electric propulsionassembly at a voltage exceeding 800 volts.

In certain exemplary embodiments, the electric power bus is configuredto transfer the electric power to the electric propulsion assembly at avoltage between about 1,000 volts and about 20,000 volts.

In certain exemplary embodiments, the electric power bus is configuredto transfer the electric power to the electric propulsion assembly at anelectrical current between about 30 amps and about 1,200 amps.

In certain exemplary embodiments, the electric power source comprises acombustion engine and an electric generator. For example, in certainexemplary embodiments, the combustion engine is at least one of aturboprop engine or a turbofan engine.

In certain exemplary embodiments, the electric propulsion assemblyfurther comprises a plurality of electric motors and a plurality ofpropulsors, each propulsor powered by a respective one of the electricmotors. For example, in certain exemplary embodiments, the electricpower bus electrically connects the electric power source to each of theplurality of electric motors, and wherein the electric power bus isconfigured to transfer electrical power to each of the plurality ofelectric motors at a voltage exceeding 800 volts.

In certain exemplary embodiments, the electric power bus comprises ahigh voltage cable configured to carry the electrical power having avoltage exceeding 800 volts. For example, in certain embodiments, thehigh voltage cable includes a conductor; a semi-conductive conductorscreen enclosing the conductor; an insulation layer enclosing theconductor screen; and a semi-conductive insulator screen enclosing theinsulation layer. For example, in certain embodiments, the high voltagecable further includes a metallic shield enclosing the insulator screen.In certain exemplary embodiments the metallic shield is a groundedmetallic shield. In certain exemplary embodiments, the power bus furtherincludes a coolant system having a cooling line, wherein at least aportion of high voltage cable extends coaxially with the cooling line.For example, in some embodiments the cooling line comprises a coolantconfigured to flow therethrough to cool the high voltage cable.

In certain exemplary embodiments, the electric propulsion system isconfigured as a boundary layer ingestion fan.

In certain exemplary embodiments, the propulsor of the electricpropulsion system is configured as a fan.

In an exemplary aspect of the present disclosure, a method for operatinga propulsion system for an aircraft is provided. The method includesgenerating electric power with an electric power source, andtransferring the electric power generated with the electric power sourceto an electric propulsion assembly through an electric power bus at avoltage exceeding 800 volts. The method also includes generating thrustfor the aircraft with the electric propulsion assembly, the electricpropulsion assembly being powered by the electric power transferredthrough the electric power bus.

In certain exemplary aspects transferring the electric power generatedwith the electric power source to the electric propulsion assemblythrough the electric power bus includes transferring the electric powergenerated with the electric power source to the electric propulsionassembly through the electric power bus at a voltage between about 1,000volts and about 20,000 volts.

In certain exemplary aspects transferring the electric power generatedwith the electric power source to the electric propulsion assemblythrough the electric power bus includes transferring the electric powergenerated with the electric power source to the electric propulsionassembly through the electric power bus at an electrical current betweenabout 30 amps and about 1,200 amps.

In certain exemplary aspects transferring the electric power generatedwith the electric power source to the electric propulsion assemblythrough the electric power bus includes transferring the electric powergenerated with the electric power source to the electric propulsionassembly through a high voltage cable, the high voltage cable includinga conductor, a semi-conductive conductor screen enclosing the conductor,an insulation layer enclosing the conductor screen, and asemi-conductive insulator screen enclosing the insulation layer.

In certain exemplary aspects transferring the electric power generatedwith the electric power source to the electric propulsion assemblythrough the electric power bus includes transferring the electric powergenerated with the electric power source to the electric propulsionassembly through a high voltage cable extending coaxially with a coolingline of a coolant system.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdescription and appended claims. The accompanying drawings, which areincorporated in and constitute a part of this specification, illustrateembodiments of the invention and, together with the description, serveto explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth in the specification, which makes reference to the appendedfigures, in which:

FIG. 1 is a top view of an aircraft according to various exemplaryembodiments of the present disclosure.

FIG. 2 is a schematic, cross-sectional view of a gas turbine enginemounted to the exemplary aircraft of FIG. 1.

FIG. 3 is a schematic, cross-sectional view of an electric fan assemblyin accordance with an exemplary embodiment of the present disclosure.

FIG. 4 is a top view of an aircraft including a propulsion system inaccordance with another exemplary embodiment of the present disclosure.

FIG. 5 is a top view of an aircraft including a propulsion system inaccordance with yet another exemplary embodiment of the presentdisclosure.

FIG. 6 is a port side view of the exemplary aircraft of FIG. 5

FIG. 7 is a schematic view of a propulsion system in accordance with anexemplary embodiment of the present disclosure.

FIG. 8 is a side, sectional view of a cable of an electric power bus ofthe exemplary propulsion system of FIG. 7.

FIG. 9 is a schematic view of a propulsion system in accordance withanother exemplary embodiment of the present disclosure.

FIG. 10 is a close-up, side, cross-sectional view of a section of anelectric power bus of the exemplary propulsion system of FIG. 9.

FIG. 11 is a flow chart of a method for operating a propulsion system inaccordance with an exemplary aspect of the present disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to present embodiments of theinvention, one or more examples of which are illustrated in theaccompanying drawings. The detailed description uses numerical andletter designations to refer to features in the drawings. Like orsimilar designations in the drawings and description have been used torefer to like or similar parts of the invention.

As used herein, the terms “first”, “second”, and “third” may be usedinterchangeably to distinguish one component from another and are notintended to signify location or importance of the individual components.

The terms “forward” and “aft” refer to relative positions within a gasturbine engine or vehicle, and refer to the normal operational attitudeof the gas turbine engine or vehicle. For example, with regard to a gasturbine engine, forward refers to a position closer to an engine inletand aft refers to a position closer to an engine nozzle or exhaust.

The terms “upstream” and “downstream” refer to the relative directionwith respect to a flow in a pathway. For example, with respect to afluid flow, “upstream” refers to the direction from which the fluidflows, and “downstream” refers to the direction to which the fluidflows. However, the terms “upstream” and “downstream” as used herein mayalso refer to a flow of electricity.

The singular forms “a”, “an”, and “the” include plural references unlessthe context clearly dictates otherwise.

Approximating language, as used herein throughout the specification andclaims, is applied to modify any quantitative representation that couldpermissibly vary without resulting in a change in the basic function towhich it is related. Accordingly, a value modified by a term or terms,such as “about”, “approximately”, and “substantially”, are not to belimited to the precise value specified. In at least some instances, theapproximating language may correspond to the precision of an instrumentfor measuring the value, or the precision of the methods or machines forconstructing or manufacturing the components and/or systems. Forexample, the approximating language may refer to being within a tenpercent margin.

Here and throughout the specification and claims, range limitations arecombined and interchanged, such ranges are identified and include allthe sub-ranges contained therein unless context or language indicatesotherwise. For example, all ranges disclosed herein are inclusive of theendpoints, and the endpoints are independently combinable with eachother.

Referring now to the drawings, wherein identical numerals indicate thesame elements throughout the figures, FIG. 1 provides a top view of anexemplary aircraft 10 as may incorporate various embodiments of thepresent disclosure. As shown in FIG. 1, the aircraft 10 defines alongitudinal centerline 14 that extends therethrough, a lateraldirection L, a forward end 16, and an aft end 18. Moreover, the aircraft10 includes a fuselage 12, extending longitudinally from the forward end16 of the aircraft 10 to the aft end 18 of the aircraft 10, and a wingassembly including a port side and a starboard side. More specifically,the port side of the wing assembly is a first, port side wing 20, andthe starboard side of the wing assembly is a second, starboard side wing22. The first and second wings 20, 22 each extend laterally outward withrespect to the longitudinal centerline 14. The first wing 20 and aportion of the fuselage 12 together define a first side 24 of theaircraft 10, and the second wing 22 and another portion of the fuselage12 together define a second side 26 of the aircraft 10. For theembodiment depicted, the first side 24 of the aircraft 10 is configuredas the port side of the aircraft 10, and the second side 26 of theaircraft 10 is configured as the starboard side of the aircraft 10.

Each of the wings 20, 22 for the exemplary embodiment depicted includesone or more leading edge flaps 28 and one or more trailing edge flaps30. The aircraft 10 further includes a vertical stabilizer 32 having arudder flap (not shown) for yaw control, and a pair of horizontalstabilizers 34, each having an elevator flap 36 for pitch control. Thefuselage 12 additionally includes an outer surface or skin 38. It shouldbe appreciated however, that in other exemplary embodiments of thepresent disclosure, the aircraft 10 may additionally or alternativelyinclude any other suitable configuration. For example, in otherembodiments, the aircraft 10 may include any other configuration ofstabilizer.

Referring now also to FIGS. 2 and 3, the exemplary aircraft 10 of FIG. 1additionally includes a propulsion system 50 having a first propulsorassembly 52 and a second propulsor assembly 54. FIG. 2 provides aschematic, cross-sectional view of the first propulsor assembly 52, andFIG. 3 provides a schematic, cross-sectional view of the secondpropulsor assembly 54. As is depicted, each of the first propulsorassembly 52 and second propulsor assembly 54 are configured asunder-wing mounted propulsor assemblies.

Referring particularly to FIGS. 1 and 2, the first propulsor assembly 52is mounted, or configured to be mounted, to the first side 24 of theaircraft 10, or more particularly, to the first wing 20 of the aircraft10. The first propulsor assembly 52 generally includes a turbomachine102 and a primary fan (referred to simply as “fan 104” with reference toFIG. 2). More specifically, for the embodiment depicted the firstpropulsor assembly 52 is configured as a turbofan engine 100 (i.e., theturbomachine 102 and the fan 104 are configured as part of the turbofan100).

As shown in FIG. 2, the turbofan 100 defines an axial direction A1(extending parallel to a longitudinal centerline 101 provided forreference) and a radial direction R1. As stated, the turbofan 100includes the fan 104 and the turbomachine 102 disposed downstream fromthe fan 104.

The exemplary turbomachine 102 depicted generally includes asubstantially tubular outer casing 106 that defines an annular inlet108. The outer casing 106 encases, in serial flow relationship, acompressor section including a booster or low pressure (LP) compressor110 and a high pressure (HP) compressor 112; a combustion section 114; aturbine section including a first, low pressure (LP) turbine 118 and asecond, high pressure (HP) turbine 116; and a jet exhaust nozzle section120.

The exemplary turbomachine 102 of the turbofan 100 additionally includesone or more shafts rotatable with at least a portion of the turbinesection and, for the embodiment depicted, at least a portion of thecompressor section. More particularly, for the embodiment depicted, theturbofan 100 includes a high pressure (HP) shaft or spool 122, whichdrivingly connects the HP turbine 116 to the HP compressor 112.Additionally, the exemplary turbofan 100 includes a low pressure (LP)shaft or spool 124, which drivingly connects the LP turbine 118 to theLP compressor 110.

Further, the exemplary fan 104 depicted is configured as a variablepitch fan having a plurality of fan blades 128 coupled to a disk 130 ina spaced apart manner. The fan blades 128 extend outwardly from disk 130generally along the radial direction R1. Each fan blade 128 is rotatablerelative to the disk 130 about a respective pitch axis P1 by virtue ofthe fan blades 128 being operatively coupled to a suitable actuationmember 132 configured to collectively vary the pitch of the fan blades128. The fan 104 is mechanically coupled to the LP shaft 124, such thatthe fan 104 is mechanically driven by the first, LP turbine 118. Moreparticularly, the fan 104, including the fan blades 128, disk 130, andactuation member 132, is mechanically coupled to the LP shaft 124through a power gearbox 134, and is rotatable about the longitudinalaxis 101 by the LP shaft 124 across the power gear box 134. The powergear box 134 includes a plurality of gears for stepping down therotational speed of the LP shaft 124 to a more efficient rotational fanspeed. Accordingly, the fan 104 is powered by an LP system (includingthe LP turbine 118) of the turbomachine 102.

Referring still to the exemplary embodiment of FIG. 2, the disk 130 iscovered by rotatable front hub 136 aerodynamically contoured to promotean airflow through the plurality of fan blades 128. Additionally, theturbofan 100 includes an annular fan casing or outer nacelle 138 thatcircumferentially surrounds the fan 104 and/or at least a portion of theturbomachine 102. Accordingly, the exemplary turbofan 100 depicted maybe referred to as a “ducted” turbofan engine. Moreover, the nacelle 138is supported relative to the turbomachine 102 by a plurality ofcircumferentially-spaced outlet guide vanes 140. A downstream section142 of the nacelle 138 extends over an outer portion of the turbomachine102 so as to define a bypass airflow passage 144 therebetween.

Referring still to FIG. 2, the propulsion system 50 additionallyincludes an electric machine, which for the embodiment depicted isconfigured as an electric generator 56. The electric generator 56 andturbofan engine 100 may generally be referred to herein as an electricpower source of the propulsion system 50. Additionally, the electricgenerator 56 is, for the embodiment depicted, positioned within theturbomachine 102 of the turbofan engine 100 and is in mechanicalcommunication with one of the shafts of the turbofan engine 100. Morespecifically, for the embodiment depicted, the electric generator isdriven by the first, LP turbine 118 through the LP shaft 124. Theelectric generator 56 is configured to convert mechanical power of theLP shaft 124 to electric power. Accordingly, the electric generator 56is also powered by the LP system (including the LP turbine 118) of theturbomachine 102.

It should be appreciated, however, that in other exemplary embodiments,the electric generator 56 may instead be positioned at any othersuitable location within the turbomachine 102 or elsewhere, and may be,e.g., powered in any other suitable manner. For example, the electricgenerator 56 may be, in other embodiments, mounted coaxially with the LPshaft 124 within the turbine section, or alternatively may be offsetfrom the LP shaft 124 and driven through a suitable gear train.Additionally, or alternatively, in other exemplary embodiments, theelectric generator 56 may instead be powered by the HP system, i.e., bythe HP turbine 116 through the HP shaft 122, or by both the LP system(e.g., the LP shaft 124) and the HP system (e.g., the HP shaft 122) viaa dual drive system.

It should further be appreciated that the exemplary turbofan engine 100depicted in FIG. 2 may, in other exemplary embodiments, have any othersuitable configuration. For example, in other exemplary embodiments, thefan 104 may not be a variable pitch fan, and further, in other exemplaryembodiments, the LP shaft 124 may be directly mechanically coupled tothe fan 104 (i.e., the turbofan engine 100 may not include the gearbox134). Further, it should be appreciated that in other exemplaryembodiments, the first propulsor assembly 52 may include any othersuitable type of engine. For example, in other embodiments, the turbofanengine 100 may instead be configured as a turboprop engine or anunducted turbofan engine. Additionally, however, in other embodiments,the turbofan engine 100 may instead be configured as any other suitablecombustion engine for driving the electric generator 56. For example, inother embodiments, the turbofan engine may be configured as a turboshaftengine, or any other suitable combustion engine.

Referring still to FIGS. 1 and 2, the propulsion system 50 depictedadditionally includes an electrical power bus 58 to allow the electricgenerator 56 to be in electrical communication with one or more othercomponents of the propulsion system 50 and/or the aircraft 10. For theembodiment depicted, the electrical power bus 58 includes one or moreelectrical cables or lines 60 connected to the electric generator 56,and for the embodiment depicted, extending through one or more of theoutlet guide vanes 140. As will be discussed in greater detail below,the electric power bus is generally configured as a high-voltageelectric power bus, such that the propulsion system 50 may generallyoperate with relatively high voltages.

Additionally, the propulsion system 50 depicted further includes one ormore energy storage devices 55 (such as one or more batteries or otherelectrical energy storage devices) electrically connected to theelectrical power bus 58 for, e.g., providing electrical power to thesecond propulsor assembly 54 and/or receiving electrical power from theelectric generator 56. Inclusion of the one or more energy storagedevices 55 may provide performance gains, and may increase a propulsioncapability of the propulsion system 50 during, e.g., transientoperations. More specifically, the propulsion system 50 including one ormore energy storage devices 55 may be capable of responding more rapidlyto speed change demands.

Referring now particularly to FIGS. 1 and 3, the exemplary propulsionsystem 50 additionally includes the second propulsor assembly 54positioned, or configured to be positioned, at a location spaced apartfrom the first propulsor assembly 52. More specifically, for theembodiment depicted, the second propulsor assembly 54 is mounted at alocation away from the first propulsor assembly 52 along the lateraldirection L such that they ingest different airstreams along the lateraldirection L. However, in other embodiments, the first and secondpropulsor assemblies 52, 54 may each be mounted to the aircraft 10 usinga common mount. With such a configuration, however, the first and secondpropulsor assemblies 52, 54 may still be positioned on the mount in amanner such that they are spaced apart from one another, e.g., along thelateral direction L such that they ingest different airstreams along thelateral direction L.

Referring still to the exemplary embodiment of FIGS. 1 and 3, the secondpropulsor assembly 54 is mounted to the second side 26 of the aircraft10, or rather to the second wing 22 of the aircraft 10. Referringparticularly to FIG. 3, the second propulsor assembly 54 is generallyconfigured as an electric propulsion assembly including an electricmotor and a propulsor. More particularly, for the embodiment depicted,the electric propulsion assembly includes an electric fan 200, theelectric fan including an electric motor 206 and a propulsor/fan 204.The electric fan 200 defines an axial direction A2 extending along alongitudinal centerline axis 202 that extends therethrough forreference, as well as a radial direction R2. For the embodimentdepicted, the fan 204 is rotatable about the centerline axis 202 by theelectric motor 206.

The fan 204 includes a plurality of fan blades 208 and a fan shaft 210.The plurality of fan blades 208 are attached to/rotatable with the fanshaft 210 and spaced generally along a circumferential direction of theelectric fan 200 (not shown). In certain exemplary embodiments, theplurality of fan blades 208 may be attached in a fixed manner to the fanshaft 210, or alternatively, the plurality of fan blades 208 may berotatable relative to the fan shaft 210, such as in the embodimentdepicted. For example, the plurality of fan blades 208 each define arespective pitch axis P2, and for the embodiment depicted are attachedto the fan shaft 210 such that a pitch of each of the plurality of fanblades 208 may be changed, e.g., in unison, by a pitch change mechanism211. Changing the pitch of the plurality of fan blades 208 may increasean efficiency of the second propulsor assembly 54 and/or may allow thesecond propulsor assembly 54 to achieve a desired thrust profile. Withsuch an exemplary embodiment, the fan 204 may be referred to as avariable pitch fan.

Moreover, for the embodiment depicted, the electric fan 200 depictedadditionally includes a fan casing or outer nacelle 212, attached to acore 214 of the electric fan 200 through one or more struts or outletguide vanes 216. For the embodiment depicted, the outer nacelle 212substantially completely surrounds the fan 204, and particularly theplurality of fan blades 208. Accordingly, for the embodiment depicted,the electric fan 200 may be referred to as a ducted electric fan.

Referring still particularly to FIG. 3, the fan shaft 210 ismechanically coupled to the electric motor 206 within the core 214, suchthat the electric motor 206 drives the fan 204 through the fan shaft210. The fan shaft 210 is supported by one or more bearings 218, such asone or more roller bearings, ball bearings, or any other suitablebearings. Additionally, the electric motor 206 may be an inrunnerelectric motor (i.e., including a rotor positioned radially inward of astator), or alternatively may be an outrunner electric motor (i.e.,including a stator positioned radially inward of a rotor).

As briefly noted above, the electric power source (i.e., the electricgenerator 56 of the first propulsor assembly 52 for the embodimentdepicted) is electrically connected with the electric propulsionassembly (i.e., the electric motor 206 and the fan 204 of the electricfan 200 for the embodiment depicted) for providing electrical power tothe electric propulsion assembly. More particularly, the electric motor206 of the electric fan 200 is in electrical communication with theelectric generator 56 through the electrical power bus 58, and moreparticularly through the one or more electrical cables or lines 60extending therebetween. Again, as will be discussed in more detailbelow, the electric power bus 58 is configured to provide relativelyhigh-voltage electrical power to the electric propulsion assembly fordriving the electric propulsion assembly.

A propulsion system in accordance with one or more of the aboveembodiments may be referred to as a gas-electric, or hybrid, propulsionsystem, given that a first propulsor assembly is configured as aturbofan engine mounted to a first side of an aircraft and a secondpropulsor assembly is configured as an electrically driven fan mountedto a second side of the aircraft.

It should be appreciated, however, that in other exemplary embodimentsthe exemplary propulsion system may have any other suitableconfiguration, and further, may be integrated into an aircraft 10 in anyother suitable manner. For example, referring now to FIG. 4, an aircraft10 and propulsion system 50 in accordance with another exemplaryembodiment of the present disclosure is depicted. The exemplary aircraft10 and propulsion system 50 of FIG. 4 may be configured in substantiallythe same manner as exemplary aircraft 10 and propulsion system 50 ofFIGS. 1 through 3, and accordingly, the same or similar numbers mayrefer to same or similar parts.

For example, the exemplary aircraft 10 of FIG. 4 generally includes afuselage 12 and a wing assembly, the wing assembly including a port sidewing 20 and a starboard side wing 22. Additionally, the propulsionsystem 50 includes a first propulsor assembly 52. The first propulsorassembly 52 may be configured as, e.g., a turbofan. The propulsionsystem 50 additionally includes an electric generator 56 mechanicallydriven by the first propulsor assembly 52 (see, e.g., FIG. 2). Moreover,the propulsion system 50 includes a second propulsor assembly 54, whichis an electric propulsion assembly. The electric generator 56 iselectrically connected to the electric propulsion assembly through anelectric power bus 58 for powering the electric propulsion assembly.

Notably, however, for the embodiment of FIG. 4, the electric propulsionassembly includes a plurality of electric motors 206 and a plurality ofpropulsors, each propulsor power by a respective one of the electricmotors 206. More specifically, for the embodiment depicted, the electricpropulsion assembly includes a plurality of electric fans 200, with theelectric power source (i.e., the turbofan engine of the first propulsorassembly 52 and electric generator 56 for the embodiment depicted)electrically connected to the electric motors 206 of each of theplurality of electric fans 200 through the electric power bus 58.

More specifically, still, the electric propulsion assembly of FIG. 4includes a first electric fan 200A mounted to the port side wing 20 ofthe aircraft 10 at a location laterally outward of the fuselage 12relative to the first propulsor assembly 52. The electric propulsionassembly of FIG. 4 further includes a second electric fan 200B mountedto the starboard side wing 22 and a third electric fan 200C also mountedto the starboard side wing 22. The second and third electric fans 200B,200C are spaced along the lateral direction L of the aircraft 10.Accordingly, for the exemplary embodiment of FIG. 4, the electricpropulsion assembly includes a plurality of electric fans 200, theplurality of electric fans 200 including at least three electric fans200.

Notably, however, in other exemplary embodiments, the electricpropulsion assembly may include any other suitable number of electricfans 200. For example, in other exemplary embodiments the electricpropulsion assembly may include two electric fans 200, four electricfans 200, or any other suitable number of electric fans 200.Additionally, the plurality of electric fans 200 may be arranged in anyother suitable manner, and attached to the aircraft 10 at any suitablelocation (including, e.g., tail mounted configurations).

Moreover, it should further be appreciated that in still other exemplaryembodiments, the propulsion system 50 and/or aircraft 10 may have othersuitable configurations. For example, referring now to FIGS. 5 and 6, anaircraft 10 and propulsion system 50 in accordance with still anotherexemplary embodiment of the present disclosure is depicted. Theexemplary aircraft 10 and propulsion system 50 of FIGS. 5 and 6 may beconfigured in substantially the same manner as exemplary aircraft 10 andpropulsion system 50 of FIGS. 1 through 3, and accordingly, the same orsimilar numbers may refer to same or similar parts.

For example, the exemplary aircraft 10 of FIGS. 5 and 6 generallyincludes a fuselage 12 and a wing assembly, the wing assembly includinga port side wing 20 and a starboard side wing 22. Additionally, thepropulsion system 50 includes a first propulsor assembly 52 and one ormore electric generators mechanically driven by the first propulsorassembly 52. Moreover, the propulsion system 50 includes a secondpropulsor assembly 54, which is an electric propulsion assembly. Thefirst propulsor assembly 52 is electrically connected to, and configuredto provide electrical power to, the second propulsor assembly 54 via anelectric power bus 58.

However, for the embodiment of FIGS. 5 and 6, the first propulsorassembly 52 includes a first aircraft engine 62 and the second aircraftengine 64. For the embodiment depicted, the first and second aircraftengines 62, 64 are configured as gas turbine engines, or rather asturbofan engines (see, e.g., FIG. 2) attached to and suspended beneaththe wings 20, 22 in an under-wing configuration. Additionally, for theembodiment of FIGS. 5 and 6, the propulsion system 50 further includesone or more electric generators operable with the engines 62, 64. Morespecifically, for the embodiment depicted, the propulsion system 50further includes a first electric generator 66 operable with the firstjet engine 62 and a second electric generator 68 operable with thesecond jet engine 64. Although depicted schematically outside therespective jet engines 62, 64, in certain embodiments, the electricgenerators 66, 68 may be positioned within a respective jet engine 62,64 (see, e.g., FIG. 2). Additionally, it will be appreciated that theelectric generators 56, 68 are configured to convert the mechanicalpower to electrical power, and provide such electrical power to theelectric propulsion assembly via the electric power bus 58.

Further, for the embodiment of FIGS. 5 and 6, the electric propulsionassembly includes an electric fan 70 configured to be mounted at the aftend 18 of the aircraft 10, and hence the electric fan 70 depicted may bereferred to as an “aft engine.” Further, the electric fan 70 depicted isconfigured to ingest and consume air forming a boundary layer over thefuselage 12 of the aircraft 10. Accordingly, the exemplary electric fan70 depicted in FIGS. 5 and 6 may also be referred to as a boundary layeringestion (BLI) fan. The electric fan 70 is mounted to the aircraft 10at a location aft of the wings 20, 22 and/or the jet engines 62, 64.Specifically, for the embodiment depicted, the electric fan 70 isfixedly connected to the fuselage 12 at the aft end 18, such that theelectric fan 70 is incorporated into or blended with a tail section atthe aft end 18.

It should be appreciated, however, that in still other exemplaryembodiments of the present disclosure, any other suitable aircraft 10may be provided having a propulsion system 50 configured in any othersuitable manner. For example, in other embodiments, the electric fan 70may be incorporated into the fuselage of the aircraft 10, and thusconfigured as a “podded engine,” or pod-installation engine. Further, instill other embodiments, the electric fan 70 may be incorporated into awing of the aircraft 10, and thus may be configured as a “blended wingengine.” Moreover, in other embodiments, the electric fan 70 may not bea boundary layer ingestion fan, and instead may be mounted at anysuitable location on the aircraft 10 as a freestream ingestion fan.

Furthermore, in certain embodiments the first and second engines 62, 64of the first propulsor assembly 52 may be configured as any suitable jetengine, such as turbofan engines, turboprop engines, turbojet engines,etc. Further, although the first propulsor assembly 52 includes two jetengines, in other embodiments, the first propulsor assembly 52 may haveany other suitable number of jet engines, with one or more of whichdriving an electric generator. Further, still, in other embodiments, thepropulsion system 50 may not include a first propulsion system 52having, e.g. jet engines, and may instead have any other suitableengine(s) for rotating generator(s) and producing electrical power(i.e., may have any other suitable power source).

Referring now to FIG. 7, a schematic view is provided of a propulsionsystem 300 in accordance with an exemplary embodiment of the presentdisclosure. The exemplary propulsion system 300 may be configured inaccordance with one or more of the exemplary embodiments discussed abovewith reference to FIGS. 1 through 6.

For the embodiment of FIG. 7, the exemplary propulsion system 300generally includes an electric power source 302, an electric propulsionassembly 304, and an electric power bus 306 electrically connecting theelectric power source 302 to the electric propulsion assembly 304. Morespecifically, for the embodiment depicted, the electric power source 302includes a combustion engine 308 and an electric generator 310. Asdiscussed above with the embodiments of FIGS. 1 through 6, in certainembodiments the combustion engine 308 may be, e.g., one or more turbofanengines (see, e.g., FIG. 2), a turboprop engines, a turboshaft engines,or any other suitable engines. The electric generator 310 ismechanically coupled to the combustion engine 308, such that thecombustion engine 308 drives/powers the electric generator 310.Moreover, for the embodiment depicted, the electric propulsion assembly304 includes an electric motor 312 and a propulsor 314, with thepropulsor 314 being mechanically coupled to and powered by the electricmotor 312. Although the electric propulsion assembly 304 is depicted asincluding a single electric motor 312 and propulsor 314, in otherexemplary embodiments, the electric propulsion assembly 304 may insteadinclude a plurality of electric motors 312 and a respective plurality ofpropulsors 314.

Further, for the embodiment depicted the propulsion system 300 isconfigured as a high-voltage propulsion system, with the electric powerbus 306 configured to facilitate transfer of electrical power atrelatively high voltages. More specifically, the electric power source302 is configured to provide electrical power to the electric power bus306, and the electric power bus 306 is configured to transfer theelectrical power to the electric propulsion assembly 304 at a voltageexceeding 800 volts (“V”). For example, in certain exemplaryembodiments, the electric power bus 306 may be configured to transferelectrical power received from the electric power source 302 to theelectric propulsion assembly 304 at a voltage between about 1,000 V andabout 20,000 V, such as between about 1,100 V and about 8,000 V.

It will be appreciated, that by transferring electrical power from theelectric power source 302 to the electric propulsion assembly 304 (viathe power bus 306) at relatively high voltages, the electric powersource 302 may be able to transfer such electrical power at a lowerelectrical current while still delivering a desired amount of power. Forexample, in certain exemplary embodiments, the electric power bus 306may be configured to transfer electrical power to the electricpropulsion assembly 304 at an electrical current between about 30 amps(“A”) and about 1,200 A, such as between about 100 A and about 1,000 A.With such an exemplary embodiment, the electric power bus 306 may beconfigured to transfer at least about 750 kilowatts of electrical powerto the electric propulsion assembly 304 and up to about twelve (12)megawatts of electrical power. For example, in certain exemplaryembodiments the electric power bus 306 may be configured to transfer atleast about one (1) megawatt of electrical power to the electricpropulsion assembly 304, such as between about one (1) megawatt ofelectrical power and about two (2) megawatts of electrical power.

Referring still to FIG. 7, for the embodiment depicted the electricpower bus 306 further includes one or more inverter convertercontrollers (“ICC”). More specifically, the electric power bus 306includes a first ICC 316 electrically connected to the electric powersource 302 at a location immediately downstream of the electric powersource 302, and a second ICC 318 electrically connected to the electricpropulsion assembly 304 at a location immediately upstream of theelectric propulsion assembly 304. Additionally, the first and secondICCs 316, 318 are electrically connected through a transfer cable 320 ofthe electric power bus 306.

The first ICC 316 may be configured to, e.g., convert electrical powerfrom an alternating current (“AC”) electric power configuration to adirect current (“DC”) electric power configuration, or vice versa.Additionally, in certain embodiments, the first ICC may also beconfigured to receive electrical power from the electric power source302 at a relatively low voltage, and transfer such electrical power tothe transfer cable 320 at a relatively high voltage. For example, incertain embodiments, the first ICC 316 may be configured to increase avoltage of the electric power received from the electric power source302 by at least 20%, such as by at least 40%, such as by at least 80%,such as by at least 100%. For example, in certain embodiments, the firstICC 316 may be configured to increase a voltage of the electric powerreceived from the electric power source 302 by up to 1,000%.Additionally, in certain exemplary embodiments, the second ICC 318 maysimilarly be configured to, e.g., convert electrical power from a DCelectric power configuration to an AC electric power configuration, orvice versa, and further may be configured to receive electrical powerfrom the transfer cable 320 at a relatively high voltage, and transfersuch electrical power to the electric propulsion assembly 304 at arelatively low voltage. For example, in certain exemplary embodiments,the second ICC 318 may be configured to decrease a voltage of theelectric power received from the transfer cable 320 by at least 20%,such as by at least 40%, such as by at least 80%, such as by at least100%. For example, in certain embodiments, the second ICC 318 may beconfigured to decrease a voltage of the electric power received from thetransfer cable 320 by up to 1,000%.

It should be appreciated, however, that in other exemplary embodiments,the power bus 306 of the propulsion system 300 may have any othersuitable configuration. For example, in other exemplary embodiments, thepower bus 306 may not include one or both of the first ICC 316 or thesecond ICC 318. For example, in certain exemplary embodiments, thetransfer cable 320 may be configured to directly electrically connectthe electric power source 302 to the electric propulsion assembly 304(i.e., the electric generator 310 of the electric power source 302directly to the electric motor 312 of the electric propulsion assembly304). Additionally, or alternatively, in certain embodiments, the firstand second ICCs 316, 318 may not be configured to substantially modifythe voltage of the electrical power provided therethrough. Accordingly,with such an embodiment, the electrical power generated by the electricpower source 302 may be transmitted and delivered through the power bus306 to the electric propulsion assembly 304 at substantially the samevoltage at which it was produced. Such a configuration may reduce anoverall weight of the system.

As stated, transferring the electric power within the propulsion system200 at relatively high voltages may allow for transferring suchelectrical power at a reduced electrical current, while still providinga desired amount of power. As will be appreciated, such a configurationmay allow for cables having a reduced thickness, or diameter, which maysave weight in an aircraft including the exemplary propulsion system300. More particularly, for the exemplary propulsion system 300 depictedin FIG. 7, such a configuration may allow for, e.g., the transfer cable320 of the electric power bus 306 to have a reduced thickness, ordiameter, to save weight. Notably, with certain exemplary propulsionsystems, the transfer cable 320 may be required to extend relativelylong distances, such that a reduced thickness, or diameter, may save anappreciable amount of weight (see, e.g., the embodiments of FIG. 1, FIG.4, and FIGS. 5 and 6).

However, it will further be appreciated that by the operating theelectric power bus 306 at the relatively high voltages, a risk of apartial discharge, or corona discharge, is increased. Moreover, giventhat the propulsion system 300 will be operating at relatively highaltitudes (i.e., with reduced ambient pressures) this risk of partialdischarge, or corona discharges, is increased even further.

Accordingly, for the exemplary propulsion system 300 depicted in FIG. 7,the transfer cable 320 of the electric power bus 306 is configured as ahigh-voltage cable configured to carry the electrical power having therelatively high voltages from the electric power source 302 to theelectric propulsion assembly 304. More particularly, referring now toFIG. 8, a sectional view is provided of a portion of a transfer cable320 in accordance with an exemplary embodiment of the presentdisclosure, as may be utilized with the exemplary power bus 306 of FIG.7. For the embodiment of FIG. 8, the transfer cable 320 includes aconductor 322, a conductor screen 324 enclosing the conductor 322, andan insulation layer 326 enclosing the conductor screen 324. For theembodiment depicted, the conductor 322 is configured as a braidedconductor, such as a braided copper wire or a braided aluminum wire.Such a configuration may provide for increased flexibility of thetransfer cable 320. Additionally, the conductor screen 324 is configuredas a semi-conductive conductor screen, and as will be appreciated, isconfigured to minimize a risk of a partial discharge or a coronadischarge generally by smoothing out an electrical field gradientsurrounding the conductor 322. It should be appreciated, that as usedherein, the term “semi-conductive” refers to generally to any materialhaving a volume resistivity between about 1 ohm-meter and about1,000,000 ohm-meters.

Notably, as for the embodiment depicted the conductor 322 is a braidedconductor, there will inherently be air gaps on an outer surface (e.g.,between strands). These air gaps, or more particularly the strandsdefining the air gaps, may provide for relatively high concentrations ofthe electric field lines at, e.g., an outer radius of the strands of theconductor 322. The conductor screen 324 disperses these relatively highconcentrations of electrical field lines and further reduces a potentialfor the air gaps to breakdown at altitude. This is achieved by eitherfilling the air gaps with the semi-conductive conductor screen 324, ormitigating the electric field gradient by effectively extending out theouter radius of the conductor 322. In certain embodiments, the conductorscreen 324 may be a carbon-impregnated material, such as acarbon-impregnated polyethylene, EPR (ethylene propylene rubber),silicon rubber, or alternatively may be formed of any other suitablematerial. Additionally, in certain embodiments, the conductor screen 324may have a thickness between about two thousandths of an inch (“mils”)and about one hundred mils. For example, the conductor screen 224 mayhave a thickness between about four mils and about fifty mils.

Additionally, for the embodiment depicted, the insulation layer 326 maybe, e.g., EPR (ethylene propylene rubber), XLPE (crosslinkedpolyethylene), or a silicone rubber insulation layer. Moreover, for theembodiment depicted, the transfer cable 320 further includes aninsulator screen 328 enclosing the insulation layer 326. The insulatorscreen 328, similar to the conductor screen 324, is configured as asemi-conductive insulator screen configured to minimize a risk of apartial discharge or a corona discharge generally by smoothing out apotential electrical field gradient surrounding the insulation layer326/dispersing relatively high concentrations of electrical field lines.The insulator screen 328 may, in certain embodiments, be configured insubstantially the same manner as the conductor screen 324 describedabove.

Notably, the transfer cable 320 further includes a metallic shield 330surrounding the insulation screen 328 and an outer sheath 330surrounding the metallic shield. The metallic shield 330 is a groundedmetallic shield (shown schematically in FIG. 8). One or both of theinsulation screen 328 and conductor screen 324 (depending on theconfiguration) provide a shallow electrical field gradient and a strongelectro-mechanical bond between, e.g., the metallic shield 330 (i.e., ametal layer) and the insulation layer 326. The outer sheath 331 may haveany suitable configuration for providing general protection for atransfer cable 320. It should be appreciated, however, that in otherexemplary embodiments, the transfer cable 320 may further haveadditional layers not described herein, or alternatively may not includeone or more of the layers described herein.

Additionally, it should further be appreciated that in still otherexemplary embodiments, the power bus 306 may have any other suitableconfiguration for transferring electrical power at the relatively highvoltages required by the propulsion system 300. For example, referringnow to FIG. 9, in certain exemplary embodiments, the power bus 306 mayfurther include a coolant system 332 for cooling one or more of thecables of the power bus 306, such as the transfer cable 320. Theexemplary power bus 306 of FIG. 9 may be configured in substantially thesame manner as exemplary power bus 306 of FIG. 7. For example, the powerbus 306 of FIG. 9 includes a transfer cable 320 electrically connectingthe electric power source 302 to the electric propulsion assembly 304,and is configured to transfer electrical power through the transfercable 320 from the electric power source 302 to the electric propulsionassembly 304 at a voltage exceeding, e.g., 800 V.

However, for the embodiment of FIG. 9, the electric power bus 306further includes the coolant system 332. The coolant system 332 includesat least a portion extending concentric with at least a portion one ormore cables of the power bus 306 (such as the transfer cable 320). Forexample, referring briefly to FIG. 10 a close-up, side, cross-sectionalview of a section of the exemplary power bus 306 of FIG. 9 is provided.As is depicted, the power bus 306 includes the transfer cable 320. Theexemplary transfer cable 320 of FIG. 10 may be configured insubstantially the same manner as exemplary transfer cable depicted inFIG. 8. However, for the embodiment of FIG. 10, the transfer cable 320further includes a sealing layer 334 for providing a watertight seal forthe transfer cable 320.

Moreover, for the embodiment depicted, at least a portion of thetransfer cable 320 extends within a cooling line 336 of the coolantsystem 330. More specifically, for the embodiment depicted, the transfercable 320 extends generally coaxially with the cooling line 336 of thesystem, such that a flow of coolant 338 through the cooling line 336 ofthe core system 330 flows around the transfer cable 320 and may operateto, e.g., accept heat from the transfer cable 320 to cool the transfercable 320. Notably, inclusion of the coolant system 330 may allow forthe use of materials within the power bus 306, and more specifically,within the transfer cable 320, that otherwise may not be capable ofwithstanding the temperature demands of the transfer cable 320. Forexample, inclusion of the coolant system 330 may allow for an insulationlayer 326 of the transfer cable 322 be formed of, e.g., a siliconerubber, or further still, of an EPR or XLPE (each of which beinglower-temperature materials than silicone rubber).

Referring now back to FIG. 9, it will be appreciated that the coolantsystem 330 of the electric power bus 306 operates as a closed loopsystem. For example, the coolant system 330 further includes a firsttransfer box 340 and a second transfer box 342, with the cooling line336 extending therebetween (and the transfer cable 320 extendingconcentrically/coaxially therewith). The first and second transfer boxes340, 342 allow for the transfer cable 320 to transition into or out of aconcentric relationship with the cooling line 336. The coolant system330 further includes an outside loop 344 fluidly connecting the firsttransfer box 340 to the second transfer box 342. Moreover, a heatexchanger 346 is positioned in thermal communication with the outsideloop for removing heat from the coolant 338 flowing therethrough. Duringoperation, coolant 334 may flow substantially continuously from thefirst transfer box 340, through the cooling line 336 to the secondtransfer box 342, and from the second transfer box 342 through theoutside loop back to the first transfer box 340 (with the heat exchanger346 operating to remove heat therefrom). Although not depicted, incertain embodiments, a pump or other means may be provided for inducingsuch flow of coolant 338 through the coolant system 330.

Notably, although the exemplary power bus 306 of FIG. 9 does not includeany ICCs, such as ICCs 316, 318, in other embodiments, one or more ICCsmay be included.

Referring now to FIG. 11, a flow diagram is provided of a method 400 foroperating a propulsion system for an aircraft in accordance with anexemplary aspect of the present disclosure. In certain exemplaryaspects, the exemplary method 400 may be utilized with one or more ofthe exemplary propulsion systems described above with reference to FIGS.1 through 10.

As is depicted in FIG. 11, the exemplary method 400 includes at (402)generating electric power with an electric power source. In certainexemplary aspects, generating electric power with the electric powersource at (402) may include rotating/driving an electric generator ofthe electric power source with a combustion engine of the electric powersource.

Additionally, the exemplary method 400 includes at (404) transferringthe electric power generated with the electric power source to anelectric propulsion assembly through an electric power bus at a voltageexceeding 800 volts. More specifically, for the exemplary aspectdepicted in FIG. 11, transferring the electric power generated with theelectric power source to the electric propulsion assembly through theelectric power bus at (404) includes at (406) transferring the electricpower generated with the electric power source to the electricpropulsion assembly through the electric power bus at a voltage betweenabout 800 volts and about 20,000 volts. Further, still, for theexemplary aspect depicted in FIG. 11, transferring the electric powergenerated with the electric power source to the electric propulsionassembly through the electric power bus at (404) additionally includesat (408) transferring the electric power generated with the electricpower source to the electric propulsion assembly through the electricpower bus at an electrical current between about 30 amps and about 1,200amps.

Moreover, as stated, the exemplary method 400 may be utilized with oneor more of the exemplary propulsion systems described above.Accordingly, although not depicted, in certain exemplary aspects,transferring the electric power generated with the electric power sourceto the electric propulsion assembly through the electric power bus at(404) may additionally include transferring the electric power generatedwith the electric power source to the electric propulsion assemblythrough a high voltage cable, the high voltage cable potentiallyincluding a conductor, a conductor screen enclosing the conductor, aninsulation layer enclosing the conductor screen, an insulator screenenclosing the conductor, and a metallic shield enclosing the insulatorscreen. Additionally, or alternatively, in other exemplary aspects,transferring the electric power generated with the electric power sourceto the electric propulsion assembly through the electric power bus at(404) may include transferring the electric power generated with theelectric power source to the electric propulsion assembly through a highvoltage cable extending coaxially with a cooling line of a coolantsystem.

Referring still to the exemplary aspect depicted in FIG. 11, theexemplary method 400 further includes at (410) generating thrust for theaircraft with the electric propulsion assembly, the electric propulsionassembly being powered by the electric power transferred through theelectric power bus. For example, in certain exemplary aspects,generating thrust for the aircraft at (410) may include rotating thepropulsor of the electric propulsion assembly with an electric motor ofthe electric propulsion assembly, with the electric motor receivingelectrical power from the electric power bus.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they include structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

What is claimed is:
 1. A propulsion system for an aircraft comprising:an electric power source; an electric propulsion assembly comprising anelectric motor and a propulsor, the propulsor powered by the electricmotor; an electric power bus electrically connecting the electric powersource to the electric propulsion assembly, the electric power sourceconfigured to provide electrical power to the electric power bus, andthe electric power bus configured to transfer the electric power to theelectric propulsion assembly at a voltage between 800 and 20,000 volts;and first and second inverter converter controllers positioned in seriesand electrically connected to the electric power source at a locationdownstream of the electric power source and upstream of the electricpropulsion assembly, the first inverter converter controller configuredto increase a voltage of the electric power received from the powersource and the second inverter converter controller configured todecrease the voltage of the electric power received from the firstinverter controller.
 2. The propulsion system of claim 1, wherein thesecond inverter controller is configured to transfer the electric powerto the electric propulsion assembly to operate the electric propulsionassembly at a voltage between 1,000 and 20,000 volts.
 3. The propulsionsystem of claim 1, wherein the electric power bus is configured totransfer the electric power to the electric propulsion assembly tooperate the electric propulsion assembly at an electrical currentbetween about 30 amps and about 1,200 amps.
 4. The propulsion system ofclaim 1, wherein the electric power source comprises a combustion engineand an electric generator.
 5. The propulsion system of claim 4, whereinthe combustion engine is at least one of a turboprop engine or aturbofan engine.
 6. The propulsion system of claim 1, wherein theelectric propulsion assembly further comprises a plurality of electricmotors and a plurality of propulsors, each propulsor powered by arespective one of the electric motors.
 7. The propulsion system of claim6, wherein the electric power bus electrically connects the electricpower source to each of the plurality of electric motors, and whereinthe electric power bus is configured to transfer electrical power toeach of the plurality of electric motors at a voltage between 800 and20,000 volts.
 8. The propulsion system of claim 1, wherein the electricpower bus comprises a high voltage cable configured to carry theelectrical power having a voltage between 800 and 20,000 volts.
 9. Thepropulsion system of claim 8, wherein the high voltage cable comprises:a conductor defining a central portion of the cable; a semi-conductiveconductor screen enclosing the conductor; an insulation layer enclosingthe conductor screen; and a semi-conductive insulator screen enclosingthe insulation layer.
 10. The propulsion system of claim 9, wherein thehigh voltage cable further comprises: a metallic shield enclosing thesemi-conductive insulator screen.
 11. The propulsion system of claim 10,wherein the metallic shield is a grounded metallic shield.
 12. Thepropulsion system of claim 8, wherein the power bus further comprises acoolant system having a cooling line, wherein at least a portion of highvoltage cable extends coaxially with the cooling line.
 13. Thepropulsion system of claim 12, wherein the cooling line comprises acoolant configured to flow therethrough to cool the high voltage cable.14. A method for operating a propulsion system for an aircraftcomprising: generating electric power with an electric power source;transferring the electric power generated with the electric power sourceto an electric propulsion assembly through an electric power bus througha cable including a conductor forming a central portion of the cable, asemi-conductive conductor screen enclosing the conductor, an insulationlayer enclosing the conductor screen, and a semi-conductive insulatorscreen enclosing the insulation layer at a reduced voltage from anoutputted voltage of the electric power source; and generating thrustfor the aircraft with the electric propulsion assembly, the electricpropulsion assembly being powered by the electric power transferredthrough the electric power bus.
 15. The method of claim 14, whereintransferring the electric power generated with the electric power sourceto the electric propulsion assembly through the electric power buscomprises transferring the electric power generated with the electricpower source to the electric propulsion assembly through the electricpower bus, the electric propulsion assembly configured to operate at avoltage between 1,000 volts and 20,000 volts.
 16. The method of claim14, wherein transferring the electric power generated with the electricpower source to the electric propulsion assembly through the electricpower bus comprises transferring the electric power generated with theelectric power source to the electric propulsion assembly through theelectric power bus, the electric propulsion assembly configured tooperate at an electrical current between about 30 amps and about 1,200amps.
 17. The method of claim 14, wherein transferring the electricpower generated with the electric power source to the electricpropulsion assembly through the electric power bus comprisestransferring the electric power generated with the electric power sourceto the electric propulsion assembly through the cable extendingcoaxially with a cooling line of a coolant system.
 18. A propulsionsystem for an aircraft comprising: an electric power source including acombustion engine and an electric generator; an electric propulsionassembly including an electric motor and a propulsor, the propulsorpowered by the electric motor; and an electric power bus electricallyconnecting the electric power source to the electric propulsionassembly, the electric power source configured to provide electricalpower to the electric power bus, and the electric power bus configuredto transfer the electric power to the electric propulsion assembly,wherein the electric propulsion assembly operates at a voltage between1,000 and 20,000 volts.
 19. The propulsion system for an aircraft ofclaim 18, wherein the transferred electric power is below 1,000 voltsalong a portion of the bus and outputted to the electric propulsionassembly at a voltage between 1,000 and 20,000 volts.